1. Field of the Invention
This disclosure relates to aquariums suitable for keeping, maintaining and displaying jellyfish.
2. Description of the Related Art
Jellyfish (colloquially referred to as “jellies” or “sea jellies”) are free-swimming members of the phylum Cnidaria. The term jellyfish can also generally refer to members of the phylum Ctenophora. Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores, are generally transparent or translucent, and exist in shallow to deep portions of all the world's oceans. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish life stages among animals in the phylum.
Jellyfish have multiple morphologies that represent cnidarian classes including the Scyphozoa, Staurozoa, Cubozoa, and Hydrozoa that make jellyfish and many more that do not. Jellyfish are found in every ocean, from the surface to the deep sea. Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.
Aurelia aurita (moon jelly, moon jellyfish, common jellyfish, saucer jelly) is one of a group of more than ten morphologically nearly identical jellyfish species in the class Scyphozoa, genus Aurelia. The medusa is translucent and it feeds by collecting medusae, plankton and mollusks with its mucusy bell nematocyst-laden tentacles and bringing the prey into its body for digestion, but is capable of only limited motion; like other jellies it primarily drifts with the current, even when it is swimming.
United States Patent Publication US 2007/0056523 entitled Aquarium for Jellyfish describes a Kreisel tank with an octagonal shape.
Greve, W., The “planktonkreisel”, a new device for culturing zooplankton. Marine Biol. 1, 201-203 (1968) was the first publication to describe a tank capable of keeping delicate gelatinous marine animals in captivity. Before this, there was no tank design capable of having water plumbed in and out for filtration that would not suck up and damage gelatinous zooplankton.
Hamner, William. Design developments in the planktonkreisel, a plankton aquarium for ships at sea. Journal of Plankton Research, Vol. 12, No. 2 (1990) pp. 397-402, describes modifications to the original planktonkreisel design in order to make it more effective for certain research projects. William Hamner is responsible for perfecting the flow rates in kreisels along with David Powell and Paul Greeves.
U.S. Pat. No. 2,744,065 entitled Home Aquarium Circulator and Aerator describes a method of circulating and aerating water in a tank using an air lift pump. Air lift pumps have been used in many applications including those in aquarium products.
A kreisel tank (kreisel means spinning top) is a circular aquarium designed to hold delicate animals such as jellyfish. These aquariums provide slow, circular water flow with a minimum of interior hardware, to prevent delicate animals from becoming injured by pumps or the tank itself. Originally a German design, the kreisel tank is characterized by the fact that it has no sharp corners. Water moving into the tank gives a gentle flow that keeps the tank inhabitants suspended, and water leaving the tank is covered by a delicate screen that prevents the tank inhabitants from getting stuck. In a true kreisel, the circular tank has a circular, submerged lid. In a pseudokreisel tank, the tanks have a curved bottom surface and a flat top surface, similar to the shape of either a “U” or a semicircle. Stretch kreisels or Langmuir kreisels feature a “double gyre” kreisel design, where the tank length is at least twice the height. Using two downwelling inlets on both sides of the tank enables gravity create two gyres within the tank. A single downwelling inlet may be used in the middle as well. The top of a stretch kreisel may be open or closed with a lid. There may also be screens about midway down the sides of the tank, or at the top on the sides.
Because of its tranquil floating motion, the jellyfish are relaxing to watch. However, the delicate nature of their physiological shape and their relative inability to navigate make them difficult to maintain in a non-commercial artificial environment. What is needed is an aquarium that facilitates keeping, maintaining and displaying jellyfish which is adapted to provide a fluid flow process that is optimized for keeping the jellyfish suspended in the fluid given their relative inability to navigate.